I. Field of the Present Invention
The present invention relates generally to torque transfer mechanisms having plural output paths, and, more particularly, to a torque transfer mechanism which transfers differing portions of the input torque to each output shaft.
II. Description of the Prior Art
There are many previously known motor vehicle drive trains constructed to include a transfer case so that the motive power provided by the engine and transmission combination can be applied to the wheels of more than one axle. Such transfer cases often include a selector for selectively transferring torque to one or both of the output shafts of the transfer mechanism. Although it has been known to transfer the torque equally to the output shafts when the input power is to be divided for use in driving the wheels on both front and rear axles, such a torque division does not necessarily provide optimum operating charcteristics for the vehicle. Rather, dividing torque in accordance with the weight distribution carried by each axle provides better traction and handling characteristics for the vehicle.
Moreover, it is well recognized that undesirable torque buildup within the drive train can occur when the wheels of each axle set are driven at the same speed. For example, during cornering, the wheels or the rear axle set travel a shorter arc through the corner and thus should not be driven at the same speed as the wheels of the front axle set. As a result, it has been known to apply an interaxle differential mechanism for dividing the torque irrespective of the relative speeds of the front and rear wheels. One known means for providing such interaxle differential driving of the axle sets can be provided by a planetary gear set.
For example, U.S. Pat. Nos. 3,492,890, 3,378,093, 3,407,893 and 3,760,922 disclose interaxle differential mechanisms utilizing a planetary gear arrangement. However, the input of each of these differential mechanisms comprises the planet carrier of the planetary gear set. As a result, the tooth load applied by the planet pinion engaging the annulus gear is the same as the tooth load applied by the planet pinion engaging the sun gear. Nevertheless, since the annulus is substantially larger than the sun gear, the torque split therebetween is uneven and cannot be adjusted to provide a more even torque split which may be desired.
Moreover, it has also been considered desirable to drive the front steering wheels of a vehicle when the vehicle is operated in a two-wheel mode. Since the engine and transmission take up a substantial amount of space, it is important that a transfer case be as compact as possible in order to fit amid the drive train and chassis components of the vehicle. Thus, many previously known transfer cases are not well-adapted for use in vehicles having front steering and front wheel drive configurations. In addition, while it has been known to provide previously known transfer cases with clutch means for selecting between full-time four-wheel drive (interaxle differential drive) and locked fourwheel drive where both output shafts are locked for rotation at the same speed, the previously known clutches substantially increase the size, complexity and weight of the transfer case.